A. The main difference among flour types is in the gluten content, which varies depending on whether the flour is made from hard wheat or soft wheat. Gluten is the protein that helps yeast stretch and rise. To achieve the best baking results, use the type of flour a recipe specifically calls for.

All-purpose flour is designed for a number of uses, including cookies, quick breads, biscuits, and cakes. A mixture of high-gluten hard wheat and low-gluten soft wheat, it comes in both bleached and unbleached forms, which can be used interchangeably.

Bread flour is an unbleached, high-gluten blend of mostly hard wheat and is best used in yeast breads.

Cake flour is made predominantly of soft wheat. Its fine texture and high starch content make it ideal for making tender cakes, cookies, biscuits, and pastries that do not need to stretch and rise much.

Pastry flour is similar to cake flour but has a slightly higher gluten content. This aids the elasticity needed to hold together the buttery layers in flaky doughs such as croissants, puff pastry, and pie crusts.

Self-rising flour is all-purpose flour that has had baking powder and salt added to it. Use it in yeast bread recipes in place of all-purpose flour by omitting salt, and in quick bread recipes by omitting salt and baking powder.

Q. Most of my recipes call for pastry flour, but I prefer using Softasilk® cake flour. How much cake flour should I use in place of pastry flour? Also, will the amount of baking powder, baking soda, or salt need to be changed?

A. Pastry flour and cake flour are both milled from soft wheat and have lower protein levels, which makes them more suitable for items that need to be tender, such as cakes, pies, and pastries.

However, recipes call for specific types of flour for a reason. At 6 percent to 8 percent, cake flour has a lower protein level than pastry flour, which ranges from 8 percent to 10 percent protein. In addition, while pastry flour is usually sold unbleached, most cake flour, including Softasilk®, is bleached to speed up the natural process of flour maturing and color lightening.

In the past, wheat was left to mature in the field, and flour was stored in silos for a while, allowing the oxygen in the air to bleach the flour naturally. These days, because farmers take their wheat to market sooner, flour millers bleach flour to speed up that maturing process.

Bleaching toughens cake flour's protein. This allows cake flour to support large amounts of sugar and fat without collapsing. But, because of this strengthening effect, substituting cake flour for pastry flour does have some physical effects. In cookies, for example, using cake flour reduces the amount that cookies spread.

Still, because of its lower protein levels, using cake flour instead of pastry flour will yield products that are more tender and possibly more crumbly. To compensate for that, you can substitute 1 cup plus 2 tablespoons of cake flour for every cup of pastry flour. Normally, you don't have to make any adjustments in the other ingredients.

Q. I see lots of recipes that call for whole-wheat flour. Can I substitute with all-purpose white flour? Would it make a difference in baking, such as a cake or muffins?

A. Substituting white flour for whole-wheat flour could make a difference in many dishes, especially in baked goods, because the flours are so different in texture, taste, and moisture content.

White flour is the ground inner kernel or endosperm of two types of wheat: high-gluten hard wheat and low-gluten soft wheat. It contains neither the bran nor the germ of whole-wheat flours.

Whole-wheat flours are available in two general types: The type labeled "whole-wheat" is usually ground hard wheat that is high in gluten and best for baking bread. Whole-wheat "pastry flour" is made from a soft wheat low in gluten and is best for cakes, muffins, biscuits, scones, pastries, and cookies.

Although bread flour and pastry flour -- either white or whole-wheat -- can't be substituted for each other, most sources say you can successfully substitute up to half of the whole-wheat flour called for in a recipe with all-purpose white flour. You may have to experiment with the amount of the liquids in the recipe as a result.

Keep in mind, however, that white flour does not contain the fiber and nutrients of whole-wheat flour. Whole-wheat flour has fewer calories and carbohydrates than white flour, and it contains five times the fiber, twice the calcium, and 25 percent more protein than white flour.

Q. When I'm doing my weekly grocery shopping, I see the words "fortified" or "enriched" on food labels. What do they mean, and what's the difference?

A. A "fortified" food is one that has had one or more nutrients added to it that it normally does not have. For example, milk is fortified with vitamin D. Orange juice can be fortified with calcium, which benefits bone health.

Other foods, such as flour, can lose important nutrients during processing. By "enriching" the food, the food processor adds back lost vitamins and minerals, so the food can still provide most of these nutrients.

However, "enriching" does not mean extra vitamins or minerals are added. Instead, a food such as breakfast cereal can use "enriched" flour and be "fortified" with added vitamins and minerals.